Acoustic device



May 22, 1928. 1,670,777

G. R. LUM

ACOUSTIC DEVICE Filed June 26; 1922 Ge7e/QA4/m y/ y UNITED STATES y 1,670,777 PATENT OFFICE.

GEORGE E. L'UM, OF NEW YORK, N. Y., ASSIGNOB TO WESTERN ELECTRIC COMPANY,

INCORPORATED, 01 NEW YORK, N.

Y., A CORPORATION OF NEW YORK.

ACOUSTIC DEVICE.

Application filed June 26,

This invention relates to acoustic devices and particularly to those employing stretched diaphragms.

In an acoustic device employing a stretched diaphragm, it is essential that the diaphragm be securely held in its periphery to prevent slipping during the stretching or tuning operation. Heretofore considerable difiiculty has been ex erienced in holdm ing the diaphragm secure y with the result that regional strains were produced which prevented accurate tuning.

An object of the invention is to provide an efficient and economical means for securing and uniformly tensioning diaphragms of acoustic devices.

In general the invention comprises a structure having. two clamping members with non-alignable corrugated surfaces between which the diaphragm is clamped and means for stretching the diaphragm to produce a predetermined natural periodicity.

In the drawings, Fig. 1 is a rear view of a transmitter embodying the invention;

Fig. 2 is a front view of the transmitter;

Fig. 3 is a sectional view of thetransmitter on the line 3-3.

Fig. 4 shows the form of the corrugations in the diaphragm clamping members. For the sake of clearness, this figure is drawn out of scale.

A diaphragm 5 is secured between clamping members 6, and 7 by means of screws 10. Both of the clamping rings present raised voluted surfaces 8 and 9 to the diaphragm 5. The general form of these surfaces is shown in Fig. 4. Looking at the clamping surfaces of rings 6 and 7 these voluted surfaces may be, in the same direction and have a small pitch, for example, 43 turns per inch, so that when they, are placed face to face, they will in efi'ect be continuously crossing and will provide uniformly distributed clamping points between which the diaphragm maybe secured. After the dia phragm is secured between the annular members 6 and 7, the stretching ring 11, which is loosely assembled in an annular recess in the ring 6, is forced against the diaphragm k 5 by means of the screws 12. The'stretching ring 11 has a rounded edge next to the diaphragm 5 and the clamping ring 7 has a corresponding recess, andwhen pressure is applied to the diaphragm 5 through screws 12 and stretching ring .11, it will be forced 1922. Serial in. 570,970.

intothe recess of clamping ring 7, to' give the diaphragm an initial stress and provide a secondary clamping means for it. The diaphragm is iven a final tension by forcing-the stretc ing rin 13 against it by means of the external y threaded nut 14, WhlCll engages the threaded inner surface of'clamping member 7. Preferably the surface of ring 13 next to the diaphragm is sloped towards its outer edge so that the d aphragm rests only on the inner edge of ring 13. The nut 14 is provided with recesses 15 so that it may be conveniently operated by a suitable tool. d aphragm in two separate stages, that is, g1v1ng it an initial tension by applying ring 11 and a final tension by app ying a radially spaced concentric ring 13, the stress is distributed over a larger area than when all of the stretching is done by one ring and danger of rupturing the diaphragm is eliminated. An air damping plate 23 is applied to the opposite side of the diaphragm, and a washer 24 of the proper thickness is clamped between the diaphragm and plate rovide the desired air space. inner iameter of this washer is substantially the same as theinner diameter of ring 13. A seriesof holes 21 are provided in the damping plate for the inward and outward flow of the air. If the diaphragm is to be used in a, push-pull transmitter of the granular carbon type, as illustrated in the drawings, the surface of each side of the diaphragm covered'by the buttons may be gold-plated so that the diaphragm may constitute a common electrode. barrier buttons of the type disclosed in application Serial No. 505,060 filed October 3, 1921, are used, it may be preferable to apply a coat of insulating material to that part of the diaphragm between the buttons or use a diaphragm of insulating material. The carbon and electrode containing chambers 16 and 17 are mounted in the wellknown manner against the diaphragm. The chamber 16 is supported on the damping plate 23 b means of a disc 18 and the damping p ate in turn is secured within the clamping ring 6 against the diaphragm by means of the annular'spider 19 and screws 20. The chamber 17 is mounted on the bridge -25. which is secured to clamping member 7 by means of screws 22. ,Both buttons may be mounted in the manner shown By stretching a The However, if

- a Patent No. 1,050,304 of January 14, 19.13,

to C. E. Scribner.

The invention claimed is: 1. An acoustic device comprising a diaphragm and a pair of clamping members aving corrugated surfaces between which said dlaphragm is. clam d, thecorru ations of one plate crossing t ose of the ot'er.

2. An acoustic device comprising a diaphragm, and a P1111 of clamping members having spirally corrugated surfaces between 'which said diaphragm is clamped the corrugations of one member crossing those of the other.

3. An acoustic device comprising a diaphragm, a pair of clam ing members hav- -mg non-alignable spira ly corrugated surfaces between which said diaphragm is clamped, and means 'for tuning the diaphragm.

4. An acoustic device comprising a diaphragm, cla'mpingrings having corrugated surfaces between which said diaphragm is clamped, andstretching means distributing the stress over a large area'of said diaphragm,-sa1d stretching means mcludmg means applied to one side of the diaphragm,

for giving it an initial tension and means applied to the opposite side of the diaphragm for stretching it to produce the desired frequency,

5. An acoustic device comprising a diaphragm a pair of clamping rings having voluted surfaces between which the diaa pair of clamping members having voluted surfaces between which said diaphragm is clamped, one of said members havmg an annular recess therein, means in the second clamping member to force said diaphragm into said recess, means associated with the first clamping member to stretch the diaphragm to produce a desired frequency, a 'dampin plate supported against one side of the diap iragm and a current varying device supported on each side of the diaphragm in operative relation therewith.-

7 The combination of a diaphragm with a mounting, comprising a pair of clamping plates having voluted surfaces between which said diaphragm is clamped, the v0- luted surface of one plate crossing that, of the other, and a plurality of tensioning rings in addition to said clamping plates for, stretching said diaphragm to produce a predetermined fre uency.

In witness w ereof, Ihereunto subscribe my name this 22nd'day of June, A. D.

' GEORGE R. LUM. 

